Helping MIke Rettig with Fuel Tanks and Back in House Hell Again

Over the course of the past couple of weeks I had decided to cough off some bucks to have a contractor take care of refurbishing two bathrooms in the house - you know, so I could spend more time building the airplane for a change. Unfortunately what I feel has become an all too common theme in America these days is that there is no quality of service anymore. Long story short, and then I will get back to some positive airplane building stuff, I ended up firing the contractor, and I am now fixing everything he screwed up. So now I get to spend time dealing with that instead of working on the plane - a pretty typical sob story for me I'm afraid. Just can't seem to catch a break to have a relatively prolonged spurt of building activety.

I guess this sort of thing kind of bleeds over into some of the same reasons I chose to build my own airplane. The only sure way for me to know the true airworthy state and condition of any airplane that I wish to fly is to be familiar enough with it by building and maintaining it myself. Anything short of that in today's world, and you are possibly putting your life or the lives of others at risk. I just can't help but feel that way after witnessing many counts of shoddy workmanship and less than competent maintenance practices from some maintenance shops over the years.

Anyway, on a positive note, I spent a short time on Saturday helping friend and fellow builder Mike Rettig do some riveting on his RV10 auxiliary fuel tanks. This was a great opportunity for me to get my feet wet with the process of working with the Proseal and the rivetting techniques for the fuel tanks. Here is the star of the show just before we commenced:

The process is somewhat the same as any other skin riveting task. The only real difference is that the stem of each rivet is covered in thick black proseal, which is the sealant that is used to keep the fuel from leaking out of the riveted metal fuel tanks. All of the ribs are coated in the thick goo and clecoed to the skin in preparation for riveting. The clecos are removed one at a time, covered in the same goo, and a rivet is placed in each hole. You use the same bucking bar, rivet gun, or squeezer process that is used for other rivets, but for the fuel tanks this is notably messier. It is also a challenge to set each rivet correctly because the rivet stem is covered in proseal, and you cannot see the shop head forming very well, since it will be covered in proseal. So you really must have a good feel for riveting and must be very familiar with how your tools are working before you get to this point in the build process.

The bucking bar gets most of dirty work, since it must be placed on the proseal-covered rivet and will inherently also get proseal on it from any nearby point of the rib or skin during the bucking process. Everything has to get wiped down after each rivet is set to keep from making a complete mess. We used Mike's 3x rivet gun shown here with a mushroom set encased with a rubber boot around the edge. I also have one of these but have not used it yet, so I was curious as to how well it would set the rivets. We discussed air pressure settings and the need to do practice riveting. After Mike had demonstrated the timing to use (about a 1 second trigger pull), I then tried it on the surface of the work bench, everything felt about the same as with my rivet gun, so we decided to proceed without doing any practice rivets before hand.

We did most of the riveting with the tank in the cradle. We started on the bottom side since that is the flatter side of the rib, and it is the easiest to buck. I worked the rivet gun while Mike did the bucking. The truth is that there were not very many rivets to set because Mike had done most of the them the night before. Only the harder to reach rivets around the nose of the tank remained. We used a fairly standard method for riveting with two people that seems to work well for most other builders. It is all done using a 3 count process. The person on the gun calls "One" when the gun is positioned over the rivet and held firmly in place. The bucker calls "Two" when the bucking bar is in position and is ready for driving. The person on the gun then calls "Three" and on completion of that count, presses the trigger on the gun to set the rivet. The bucker then checks the rivet and calls for additional driving of the rivet if needed, or verifies if the rivet is good or needs to be drilled out, which is not something you want to do when doing the fuel tanks.. Then you wash, rinse, and repeat the process for the next rivet, after cleaning up the tools as needed.

Here is a pic of the ribs all prosealed and clecoed in place. Mike had prosealed them all in place the night before, to allow the proseal to stiffen up just a bit for riveting.

Next are some more details about the riveting process. First you remove the cleco, and then the rivet gets inserted into the hole. In most cases, pulling the cleco out of the hole draws sufficient proseal into the hole so you don't necessarily have to pre-coat the rivet first, but sometimes you need to do this if the hole is dry for some reason. Once the rivet is inserted into the hole, a hefty amount of proseal will come out of the hole, covering the dimple and most of the rivet head. The rivet is checked fo proper seating in the dimple and excess proseal is wiped away. Occasionally we had to use the rivet gun to lightly tap a rivet into its final resting place in the dimple, but most of them inserted right into the hole with no problem. You use your finger pressure to ensure that the rivet is as far down in the dimple as possible. Then the gun is placed on the rivet head and the bucking process commences. Afterward, you get a result that looks like this on the manufactured side of the rivet:

For leading edge ribs it is easiest to start on the bottom which is flatter, followed by the top. The most challenging rivets to set are always the two most forward rivets, since they are the ones that are formed around the extreme curved edge of the skin. Even setting the gun in the correct position on these rivets is a bit of challenge, since the goal is to place the mushroom flat rivet set at a 90 degree angle to the manufactured head of the rivet. Trying to figure out what 90 degrees is to a curved surface simply by eyeballing it is a bit tricky, but you can generally figure out the angle by looking at it.

Another key detail item concerns using the cradle when riveting the tanks or leading edges. While the manufactured heads were relatively easy for me to reach with the gun while the tank was in the cradle, bucking them is another story. Mike was standing on a small step ladder to allow him to get up high enough to be able to comfortably reach down inside the tank to buck the rivets. With me pushing on the rivet gun to maintain pressure while setting the rivet, Mike also had to push back on the tank with his free hand to keep the tank from sliding out of the cradle. This was a bit of trick, but he had obviously figured out how to manage it very well. Just another in a long line of acrobatic contorsionistic moves that one must make to complete this job properly.

When it came time to do the most forward rivets, we needed to take the tank out of the cradle and lay it down on a blanket on the work bench. The only other option is to raise it up out of the cradle so the nose is high enough to get the rivet gun in there. But by the time you do that, you lose all of the holding power of the cradle, so it essentially becomes useless and is more inthe way than anything at that point.

The black marks around the rivet heads in the above pic are easily cleaned up with acetone, as long as the proseal is still wet. So this has to be done soon after the rivets are set. The last two pics show the completed fuel tank rivets after cleaning off the excess proseal on the exterior:

Note the little black ring around the rivet heads in the above pic. This pic is a bit deceiving since it shows the reflection of the speckels on the epoxy floor, so just ignore that and focus on the flush rivets. This is a sign of a properly sealed rivet head on a fuel tank. I was pleased with the way this turned out. Mike is not using tank dimple dies on his tanks, and while some rivets do sit proud from time to time, all of these rivets that we set seemed to be nice and flush with the skin, so I am now more confused than ever as to the never-ending-debate about using special tank dies or regular dimple dies for the fuel tank dimples. I purchased a set of tank dies long ago, and I am still mulling over if I am going to use them or not.

On a cleanup and shop prep note - you will need lots of rags, paper towels, and most importantly rubber gloves. You need to stage these items in such a way that you can use or shed them when necessary and dawn new ones to keep everything as clean as possible. Proseal is some very sticky stuff, and it has to be when you consider that it must be resilient enough to withstand aviation grade fuel. Tools and clecoes get cleaned up after all the work is done.

Thanks Mike for the opportunity to help out with this. What a great experience. Lots of builders make this one of the 49% of the entire build that can be literally built by someone else, and still qualify as a homebuilt airplane that was "built" by you, as required for issuance of an Experimental Airworthiness Certificate. I plan on doing my own tanks, and being able to get some hands on with another builder helps emmensely with understanding what it takes to do this successfully.

Left Wing LE Stall Warning Parts and Instructions

Yesterday I managed to start the process of fluting and straightening the flanges of the inboard W408-1 L rib. I am still not 100% satisfied with it, and it is  a little bit harder to work with since it is a thicker rib than the others, but a little more tweaking and I should have it just about right. The holes will be match drilled with the W423 tank attach strip I mentioned in the previous post.

Then I focused my attention on the stall warning kit that came with my wing kit. There are electronic and fabricated aluminum parts that make up the attach bracket for this assembly, which is basically a micro switch with a flat metal vane that sticks out of the LE of the left wing at an angle such that, when the angle of the wing against the direction of flight gets too steep, the vane will move causing the microswitch to close which then sends an elecrical current to an audible warning circuit that gets piped to the audio panel, and finally to your headset. It is an early warning system designed to tell you when you about to stall the aircraft.

The only problem with installing such a devise on an aerobatic airplane such as mine is that it will be going off quite a bit as you enter different attitudes during various aerobatic maneuvers. So it basically can become more of a nuisance and  distraction during aerobatic flight, and is not recommended. 

The one interesting thing about this kit is that it contains a short support rib for the extreme leading edge of the wing that I may decide to use to help support that area since it is the same part of the LE that will house the fake machine gun fairings. One other thing I found interesting is that there is a slot that has to be created right on the lower portion of the leading edge of the wing for the vane to stick out into the airflow. According to the instructions, the slot is made by drilling 2 holes in an exact location determined by a drilling template, and then enlarging those holes with a number 10 drill bit, and then cutting the slit in between the two holes. This is a rather large hole, and I think it is more than large enough to fit two 16 ga. wires for the lights. More importantly, I was a little worried about drilling extra holes in the LE of the wing until I started looking at the stall warning kit.

The whole reason I started reviewing the details of this kit was that the holes are already predrilled for the mini support rib as well as the starter holes for the stall warning vane. Most builders not using this system will simply close the holes with a rivet or some other means. Those that will do alot of aerobatic flight or that will use an AOA system for stall warning indication instead of this system are the ones that typically will not use this kit. Vans provides it as a standard part of the wing kit, and it still makes a good backup system, if nothing else, so I may still assembly it and run wires for it except for installing the vane. The other reason I started looking at it is that the access panel opening has also already been cut out by the factory, and I will definitely be using this panel for access to the wiring for the machine guns and also possibly the stall warning switch assembly. Another added use will be for access to the wiring and fuel pump assembly for the extended range fuel tanks should I decide to install those later on. All of that stuff will also live in the same bay in the wing.

Now for some pics:

Here is the mounting bracket for the access panel clecoed into position in hole that is already cutout in the bottom of the left wing LE. There are two tabs on the left side that line up with holes for the rib flange on that side. Only problem is the instructions show this incorrectly, or they cut the aprt and drilled it incorrectly. Either way, the instructions and the actual alignment of the part do not jive with each other. Just another opportunity for Vans to straighten out some of their instructions I guess. Another part is just barely visible on the bottom of this pic. It is the template for drilling the holes in the LE of the wing for the support riblet and the slot for the vane. I guess they provide this template for those that may decide to add it later if they choose not to install it during the initial build, but in my case the holes and access panel are already cut and drilled, so I really did not need the template, but I am glad they provided it. The reason is that this template is made from .020 aluminum (or perhaps even thinner), and so it wraps around the the LE wing skin relatively easily. I went ahead and installed it for 2 reasons:
1. To see if the template holes lined up with the predrilled holes in the skin, which they did
2. To give me  a sense for the same type of "boot" that I will be fabricating that will wrap around the top and bottom of the LE wing skin, jsut as this template does.

NExt pic shows the rest of the template as it wraps around the bottom of the LE wing skin. There are two sets if template holes - one for the RV9 and the other for the RV7 and 8. You need to be sure to use the correct hole pattern. You can just see the clecoes for the holes for the bottom of the support riblet on the bottom left side of the pic, adn the unclecoed holes for the RV9 on the right side.

Next is a side shot showing the clecoed template as it wraps around the nose. The bottom - most clecoes are for the two starter holes for the vane that sticks out into the airflow that actuates the micro switch when close to the critical angle of attack of the wing.

And finally the top side of the LE wing skin showing the last set of holes for the top of the support riblet clecoed in place. It was very easy for me to invision what the mounting bracket for the gun assembly will look like after viewing this template assembly. It will simply become a question of how many nut plates and screws to use on the top and the bottom, and how far back from the LE the mouting bracket will extend, and how wide to make it.

Here is the support riblet that mounts into the LE wing skin. The micro switch is assembled with some additional brackets, the microswitch, and mounting hardware that all comes with the kit.

And here it is clecoed into position. You can also see the two starter holes for the vane that actuates the microswitch. It's really kind of a neat setup.

And finally a couple of pics that show the template after I removed it from the LE (It was completely flat when I started):

Left Wing Leading Edge Assembly

Some of my followers have mentioned to me that they are "concerned" that have not shown much actual airplane assembly progress of late, so this post is for them. After widening out the support brackets for my LE cradle, I decided I wanted to check the clearance to determine if it was  wide enough to allow the assembly of the leading edge ribs and skins. I got down the left wing LE from the shelf, made sure my door seal material was in place, and fit the LE wing skin into the cradle. It  took a fair amount of sqeezing the skin together to make it skinny enough to fit between the brackets, but it seemed to go on without too much fuss. It is a stressed skin similar to the skins on the empennage, so it requires compression to fit around the ribs.

As shown below, even though there are several voids in the brackets, the skins seemed to fit just fine, and the 1/8 inch rubber door seal material I found seemed to work perfectly as an anti-scratch lining for each bracket.It also grabs the skin to keepit from slipping a whole bunch, so I really like that solution.

After the skin was in place, I took the LE ribs and decided to doa trial fit.I was not really following directions in the plans - I just wanted to see things would fit together OK or not.My overall concern is that many builders have difficulty clecoeing the ribs in place, even with the help of the cradle. I think Vans recommends a procedure of starting at the trailing edge and moving forward on one side, and continuing from the front to the back on the other side. Another instruction is to remove all the vinyl to ensure that the rib holes line up with the skin holes correctly, but I think this may be more critical for the fuel tanks. I decided not to go to all that trouble adn just wanted to see how easily or difficult it would be to fit the ribs to the LE skin with the vinyl still in place.

I started attaching ribs to the skin from the outboard end, and I did start from the aft end on the bottom, which of course tends to be a bit flatter than the top side of the wing which is curved more than the bottom. As I got to the nose of each rib I would put clecoes in every hole, and would space them out by every other hole as I moved further aft on either side. I did have problems trying to wrap around to the other side after reaching the nose of each rib, and I found that if I clecoed the third or fourth hole aft of the tip on the top side, that allowed me to go back and cleco the remaining holes near the tip of the LE fairly easily. I was also quite pleased about the alignment of the holes in each rib and the skin, which means that all that time I spent straightening the ribs and ensuring that the rivet holes were aligned really paid off.

Here is the final nose rib on the outboard end. The overhang on the skin and additional holes are fot the Wing tip, which is basically the final step in the entire wing assembly process.

Next are a couple of shots of the most inboard rib of the LE, which I think is designated part number 408 L. This rib is unique from all the others because it is slightly thicker, is not predrilled with rivet holes, and is also about .032 inches smaller in circumferance than the others because there is an additional .032 inch thick joiner strip that is inserted between this rib and the skin. This joiner strip is then drilled for screws and nut plates that will attach the outboard end of the fuel tank to the inboard end of the wing LE.

Because the inboard rib is not predrilled with any holes, this is also the only rib that I have not straightened or fluted yet. I needed to clamp the rib onto the skin first to see where the holes generally line up, and the sharpee marks that you see in the folliwing pics on the side of the rib are the locations between the holes in the skin where I can sfely fulte the rib to straighten it.

Here is shot of rib flange from the inside of the LE skin - nice and square. Stupid digital picture won't flip the pic the right way, but you get the idea.

Here is the entire left wing LE all clecoed up and in the cradle. I have to admit that my next real construction step is to prep and prime all the main ribs and then rivet them to the front and rear spar. This LE assembly, however, was a nice departure, and something that also needed to be done sooner or later.

The LE ribs in a line:

The nose rib flanges seem to be seating fairly well with the skin, even with all the vinyl still in place:

And the finally the real reason why I wanted to assemble the LE!

Very cool.